Method of manufacturing pressure withstanding pipe

ABSTRACT

An improved pressure-withstanding pipe according to the invention is made of a soft synthetic resin or rubber material with hard synthetic resin reinforcing bodies helically wound and embedded in the pipe wall at predetermined intervals. A thin reinforcing belt member is also helically wound and embedded in the pipe wall and the opposite side end portions of the belt are anchored in adjacent ones of the rigid reinforcing bodies. The method of manufacturing a pipe according to the invention includes a step of extruding the pipe forming body by feeding rigid synthetic reinforcing material and soft synthetic material to the extruder and, at the same time, passing the thin reinforcing belt member therethrough. The resultant pipe according to the invention is highly resistant to extension and other deformation due to pressure exerted from the material being transported as well as highly resistant to external pressure and deformation from such pressure.

This is a division of application Ser. No. 896,147 filed Aug. 13, 1986,now U.S. Pat. No. 4,796,672.

BACKGROUND OF THE INVENTION

The present invention relates to pipes suitable for pneumatictransportation, or the like. The material to be transported may bemainly a liquid such as water, oil, liquid chemicals, or the like, agaseous body such as air, gas, or the like, agricultural products suchas grain, corn, or the like, or waste materials in a factory, or thelike. The present invention relates particularly to pipes which havesuperior pressure-withstanding properties and which are suitable for thetransportation of a liquid, gaseous body, grain, or the like, whichproduces a high pressure in the pipes. The present invention alsorelates to a method for manufacturing such pipes.

Conventionally, a pressure-withstanding pipe has a pipe wall with a mainportion thereof made of a soft synthetic resin material. In addition,reinforcing filaments made of a hard synthetic resin material orreinforcing wires made of metal are helically embedded in the pipe wallas a reinforcing body. Such a pipe is known and manufactured. Further, apipe of this kind having a large number of natural fiber filaments,metal wires, or the like, further embedded and arranged in parallel toeach other and disposed all over the circumferential surface of the pipewall is also known.

A pipe in which a fiber reinforcing belt is embedded in the pipe wall byusing cloth in place of the fiber filaments or wires in the pipementioned directly above also is known.

Further, it is possible to consider a method of manufacturing a pipe(OA) in which a fiber reinforcing belt is embedded in the pipe wall inaddition to such reinforcing filaments as shown in FIG. 19, for example.In this method, a belt body (01a), which is made of a soft syntheticresin material and in which hard synthetic resin reinforcing filaments(02) are embedded, is extruded from a synthetic resin extruder andhelically wound, with adjacent windings being joined by fusing adjacentedge portions with each other; then a fiber cloth reinforcing belt (03)is helically wound on the outer circumferential surface of the belt body(01a) at the same pitch as that of the belt body (01a) while partiallyoverlapping or abutting adjacent edge portions of the reinforcing belt(03); and then a soft synthetic resin flat belt body (01b) formed bybeing extruded by another synthetic resin extruder is helically wound onthe outer surface of the reinforcing belt (03) at the same pitch as thatof the belt body 01a. Again, as the belt body (01b) is wound, the endportions of adjacent windings are joined with each other by fusing.

In the case of employing such a method, however, complicated mechanicalequipment is required as there are three winding operations. Inaddition, the produced pipe (OA) is disadvantageous in that the positionwhere the soft reinforcing filaments (02) are embedded becomes thick andit is difficult for the embedded fiber reinforcing belt (03) to befirmly maintained in the pipe wall, particularly at the overlappedportion (or the abutted portion) of the side edge portions thereof.Therefore, the embedding state of the belt (03) is apt to becomeunstable. Further, particularly in the case where the pipe is used fortransporting a liquid or the like providing a high pressure in the pipe,the overlapped portion (or the abutted portion) located between theinner and outer soft belt bodies (01a) and (01b) is apt to cause apeeling phenomenon between the belt bodies. This peeling phenomenon isdue to an expansion action exerted in the circumferential or radialdirection of the pipe and an extension action exerted in thelongitudinal or axial direction of the pipe due to pressure exerted onthe pipe by the transported material in a radial and an axial direction,respectively. The peeling phenomenon can also be caused by tensilestresses which may be created when the pipe is placed in a curved state.In addition, the overlapping portion of the fiber reinforcing belt (03)is apt to slide upon generation of the extension action of the pipe soas to prevent the extension phenomenon of the pipe.

SUMMARY OF THE INVENTION

An object of the present invention is therefore to provide apressure-withstanding pipe in which all the above-mentioneddisadvantages are eliminated even where the pipe is provided with areinforcing body and a reinforcing belt body in its pipe wall.

Specifically, an object of the invention is to achieve a pipe which hasa high resistance to pressure exerted from within as well as without thepipe body.

A further object of the invention is to achieve a pipe which isresistant to the peeling phenomenon and sliding phenomenon mentionedabove.

Another object of the invention is to achieve a pipe which is easy tomanufacture, low in cost and lightweight.

The invention is an improved pressure-withstanding pipe and a method ofmanufacturing such a pipe. The improved pipe includes a pipe body havingrigid reinforcing bodies and a soft reinforcing thin film embedded inthe pipe body. The rigid reinforcing bodies are spaced at predeterminedintervals. Opposite side end portions of the soft reinforcing thin filmare embedded in adjacent ones of the rigid reinforcing bodies such thatthe reinforcing thin film lies between the adjacent ones of the rigidreinforcing bodies and has its opposite side end portions firmlyanchored therein.

The method of forming an improved pipe according to the inventioninvolves the steps of: extruding a pipe forming belt body or roll byfeeding rigid reinforcing material and soft synthetic material to anextruder and at the same time passing a continuous band of a thinreinforcing belt material therethrough; helically winding the pipeforming belt body around a pipe forming shaft such that adjacent edgeportions of the belt body are abutted or overlapped; and fusing theadjacent edge portions of the belt body.

The resultant pipe has superior structure and pressure-withstandingcharacteristics. It is also simple to manufacture and low in cost.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned objects, advantages and features of the invention aswell as other objects, advantages and features of the invention willbecome more evident with reference to the detailed description of thepreferred embodiments herein and with reference to the accompanyingdrawings in which:

FIG. 1 is a partially cut away view of an embodiment of a pipe accordingto the invention;

FIG. 2 is a perspective view of a pipe forming belt body for forming thepipe shown in FIG. 1;

FIG. 3 is an enlarged, cross-sectional view of a pipe wall of the pipeshown in FIG. 1;

FIG. 4 is a perspective view of a reinforcing belt member of a typewhich can be used in a pipe according to the invention;

FIG. 5 is a schematic and explanatory view of a device for manufacturinga pipe according to the invention;

FIGS. 6, 8, 10, 12, 14 and 16 are each cross-sectional views of a beltbody of various respective embodiments of the invention;

FIGS. 7, 9, 11, 13, 15 and 17 are each cross-sectional views of arespective pipe wall formed from the respective belt bodies of FIGS. 6,8, 10, 12, 14 and 16;

FIG. 18 is a cross-sectional view of a pipe forming belt body accordingto another embodiment of the invention;

FIG. 19 is a cross-sectional view of a pipe wall of apressure-withstanding pipe to illustrate a pipe of the type made byconventional means;

FIGS. 20-22 are respective cross-sectional views of reinforcing beltmembers of different types which can be used in a pipe according to theinvention; and

FIG. 23 ia a cross-sectional view of a belt body of an additionalembodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIGS. 1 through 4, there is shown a pressure-withstandingpipe according to a first embodiment of the invention. The pipe is madeof a soft synthetic resin material or a rubber material 1a and providedwith hard synthetic resin reinforcing bodies 2 helically embedded atpositions so as to be concealed by at least an inner surface 11 of apipe wall 1 of the pipe A. The resin reinforcing bodies 2 are disposedat a predetermined interval from each other, and a thin film reinforcingbelt member 3 is embedded in the pipe wall 1 at a position betweenadjacent ones of the hard synthetic resin reinforcing bodies 2. Withreference to FIG. 2 in particular, left and right opposite end portions3a and 3b, respectively, of the thin film reinforcing belt member 3 areembedded in left and right hard synthetic resin reinforcing body halves2a and 2b, respectively.

Referring to FIGS. 1 through 5, the method of manufacturing apressure-withstanding pipe will now be described. A pipe forming beltbody B is continuously extruded through an extruding opening 21 of anextruding molding machine C. The belt body B is made of a soft syntheticresin material or a rubber material 1a and is extruded such that is hasa predetermined width and a cross-section which is elongated in adirection which would be parallel to the axial direction of the finishedpipe. Further, the extrusion of the pipe forming belt body is such thatleft and right rigid synthetic resin reinforcing body halves 2a and 2bof a hard resin reinforcing material 1b are disposed at a predeterminedpitch and at positions in the belt body B so as to be concealed by atleast a bottom surface 111 of the material 1a and so as to be close toleft and right opposite end portions (3a,3b) of the material 1a,respectively. In addition, a reinforcing belt member 3 is passed throughthe extruder at the same time as the soft and hard resin materials suchthat the belt member 3 is embedded in the soft resin material 1a at aposition between the left and right reinforcing body halves 2a and 2b.The left and right opposite end portions 3a and 3b of the thin filmreinforcing belt member 3 are embedded in the left and right rigidsynthetic resin reinforcing body halves 2a and 2b, respectively. Theextruded belt body B is then successively guided and helically woundonto a pipe forming body or shaft 22 such that the bottom surface 111which conceals the rigid synthetic resin reinforcing body halves 2a and2b is made to correspond to the inner surface side 11 of the resultantpipe A. It should be noted that the pipe forming belt body B could bewound such that the top surface 112 corresponds to the inner surfaceside 11 of the pipe A, if the rigid synthetic resin reinforcing bodyhalves 2a and 2b are concealed at the top surface 112. While the pipeforming belt body B is helically wound, adjacent of left and right edgeportions of adjacent windings of the belt body B are abutted againsteach other or overlapped with each other. The adjacent edge portions ofadjacent windings of the belt body 3 are then fixed to each other toconnect the windings integrally.

The thin film reinforcing belt member 3 is entirely embedded in the softsynthetic resin or rubber material 1a in manufacturing the pipe formingbelt body B so that the belt body B has a good stability, in that thethin film reinforcing belt member 3 is positioned in the state where theopposite end portions 3a and 3b thereof are entirely embedded in therigid synthetic resin reinforcing bodies 2 and are surely, firmly, andextremely stably held by the reinforcing bodies 2. The opposite side endportions 3a and 3b are thereby prevented from coming out of the rigidsynthetic resin reinforcing bodies 2 even when the pipe experiencesextension in the longitudinal direction due to inner pressure. Theopposite side end portions 3a and 3b are also embedded in adjacent onesof the reinforcing bodies 2 so as to maintain the adjacent ones of therigid synthetic resin reinforcing bodies 2 at a predetermined intervaland thereby prevent the pipe from being extended excessively. Further,in manufacturing the pipe A, the pipe A can be integrally formed bymerely winding the pipe forming belt body as formed according to theabove process due to the unitary belt body structure.

Referring to the drawings, preferred embodiments according to thepresent invention will now be described in more detail.

FIGS. 1 through 3 are views showing the structure of an embodiment ofthe pressure-withstanding pipe; FIG. 5 is a schematic view showing anexample of the device for manufacturing a belt body B with which thepressure-withstanding pipe A shown in FIGS. 1 through 3 is produced; andFIG. 4 is a view showing a natural fiber cloth belt member as an exampleof the thin film reinforcing belt member 3.

In FIG. 5, the reference numeral C1 designates a hopper for feeding asoft synthetic resin material 1a therethrough, C2 a hopper for feeding ahard or rigid synthetic resin material 1b therethrough, and 23 a drumaround which the natural fiber cloth belt member 3 shown in FIG. 4 iswound. The soft synthetic resin material 1a, the rigid synthetic resinmaterial 1b and the cloth belt member 3 are integrally extruded in theform of a belt from an extruding opening 21. As shown in FIG. 2, theresultant extruded belt body B is arranged such that the cross-sectionthereof is elongated toward the left and right ends thereof, so as to beshaped, for example, in the form of an elongated parallelogram. The mainportion of the belt body B is made of the soft synthetic resin material1a. The left and right rigid synthetic resin reinforcing body halves 2aand 2b, each having a semi-circular cross-section, are embedded in thesoft synthetic resin material 1a at the left and right ends of thematerial 1a such that the respective flat, cut end surfaces of the leftand right hard synthetic resin reinforcing body halves 2a and 2b areexposed at the left and right outer end surfaces of the material 1a. Theexposed cut end surface of the reinforcing body halves 2a and 2b arepositioned at depths intermediate of the bottom and top surfaces 111 and112, respectively, of the belt body B which correspond to the inner andouter surfaces 11 and 12, respectively, of the pipe wall 1, as shown inFIGS. 1-3.

The natural fiber cloth belt member 3 serves as a thin film reinforcingbelt member in the soft resin material 1a of the belt body B and isembedded therein between the reinforcing body halves 2a and 2b with theopposite side end portions 3a and 3b of the cloth belt member 3 embeddedin the rigid resin reinforcing body halves 2a and 2b, respectively. Inthis case, if the belt member is a narrow cloth belt member 3, ratherthan that obtained by cutting wide cloth, and the belt member 3 has woofwoven-back portions 3c at the opposite sides 3a and 3b thereof, as shownin FIG. 4, the woven-back portions 3c function in the hard resinreinforcing body halves 2a and 2b, so that the belt member 3 is moresecurely and effectively held by the hard resin reinforcing body halves2a and 2b.

The thus arranged belt body B is continuously extruded from theextruding opening 21. Immediately after being extruded, such thatadjacent of the left and right end portions of the belt body B are stillsoft, the belt body B is guided onto a pipe forming body or shaft 22 ofa pipe forming machine, as shown in FIG. 5 for example. The belt body Bis then successively wound around the shaft 22 such that the adjacent ofthe left and right edge portions of the belt body B contact each other.While the belt body B is being wound around the shaft 22, the contactingadjacent edge portions of the belt body B are fused to each other sothat the wound belt body B is serially integrally connected, as shown inFIG. 3, to thereby produce such a pressure-withstanding pipe A as shownin FIG. 1. If the steps of helically winding and fusing are performedafter the left and right edge portions of the belt body B havesubstantially hardened, the step of fusing may include heating of theleft and right edge portions of the belt body B such that the edgeportions are softened.

As the synthetic resin material according to the present invention, asynthetic resin material in a group of vinyl chloride or a syntheticresin material such as polyethylene, polypropylene, or the like, in agroup of polyolefine is mainly used for both the hard and soft materialsfrom the viewpoint that they are superior in economical property,weather-proof, and the like, but any other synthetic resin may be used.Further, to achieve good affinity between the soft and hard syntheticresin materials, it is preferable to use synthetic resin materials inthe same group for the soft and hard synthetic resin materials. Inaddition, as the material for forming a main portion of the belt body Baccording to the present invention, that is, the pipe wall 1 of thepressure-withstanding pipe A, not only a soft synthetic resin materialbut also a material in a group of synthetic or natural rubber can beused.

Further, in the above-mentioned embodiment, particularly as shown inFIG. 2, in the case where the hard or rigid synthetic resin reinforcingbody halves 2a and 2b are formed so as to be exposed at the left andright edge surfaces of the belt body B, it is desirable to use a hardsynthetic resin material which per se has good fusibility, for example,a resin material from the above-mentioned group of polyethylene, or thelike.

Further, there are synthetic resin materials which have poor fusibilitywhen existing in a hard synthetic resin material state, and therefore inthe case where, for example, a hard synthetic material in a group ofvinyl chloride is used, the belt member B is formed to have such anarrangement that one or both of the hard resin reinforcing body halves2a and 2b are embedded without being exposed at the left and right sidesurfaces of the belt body B such that the soft synthetic resin material1b exists on the cut or flat surface side of the rigid resin reinforcingbody halves 2a and 2b, as shown in FIG. 6. Thus, it is possible toobtain such a pipe A in which the soft synthetic resin material 1bexists between the hard resin reinforcing body halves 2a and 2b so thatthe adjacent left and right edges of adjacent windings of the belt bodyB (which correspond to left and right side surfaces of the belt body B,respectively) are securely joined by fusing all over the adjacent edgesthereof. A cross-sectional view of a pipe wall 1 formed using the beltbody of FIG. 6 is shown in FIG. 7.

As the thin film reinforcing belt member 3 according to the presentinvention, in addition to the natural fiber cloth belt member as shownin the above-mentioned embodiment, synthetic resin fiber, glass fiber,carbon fiber, and the like, which have poor fusibility, that is, whichcan be fused at a high temperature, may be used as a fibrous materialfor the belt member. These materials may be used alone or in anycombination thereof, and the fibrous kind may be either a multi-filamentmaterial or a mono-filament material.

In addition, braids, non-woven cloth, or the like, may be used in placeof the cloth. Not only fibrous materials but also materials of metalfilaments such as wires may be used as the material for the belt member.Further, a thin metal plate of a material such as steel, stainless steelor the like, or such a thin plate bored with small holes in the form ofa punched metal plate may be used as the material for the belt member.In the case of using the belt member made of thin metal plate, the leftand right opposite side end portions 3a and 3b of the belt member 3 maybe straight, as shown in FIG. 22, or bent in an L-shape, a V-shape, acurled-shape, or the like, as shown in FIGS. 20 and 21. In this way, itis possible to ensure the fixing between the embedded hard resinreinforcing body halves 2a and 2b and the belt member 3 at the oppositeside end portions 3a and 3b thereof.

FIGS. 8 and 9 show an embodiment of the pipe A formed such that a beltbody B, in which rigid resin reinforcing body halves 2a and 2b arepartly projected from the top surface 112 of the belt body B in FIG. 8,is wound to form the pipe A such that the lower surface 111 of the beltbody B becomes the inner surface 11 of the pipe A.

In an embodiment shown in FIGS. 10 and 11, a pipe A is formed by a beltbody B which is arranged such that rectangularly shaped rigid resinreinforcing body halves 2a and 2b are exposed at the left and right sidesurfaces and the top surface 112 of the belt body B. In accordance withthe embodiments discussed above, the bottom surface 111 of the belt bodyB corresponds to the inner surface 11 of the pipe A. Further, in theembodiment of FIGS. 10 and 11, the belt body B has a thin filmreinforcing belt member 3 embedded therein such that the opposite sideend portions 3a and 3b of the belt body B intersect the rigid resinreinforcing body halves 2a and 2b and have left and right outermost edgeportions 33a and 33b, respectively, which are slightly projectedoutwardly from the left and right reinforcing body halves 2a and 2b,respectively. The pipe wall 1 is then formed such that the leftoutermost edge portion 33a is further disposed in the right rigid resinreinforcing body half 2b of the adjacent winding to the left, as shownin FIG. 11. Similarly, the right outermost edge portion 33b is furtherdisposed in the left body half 2a of the other adjacent winding to theright.

As described above, the way in which the opposite side end portions 3aand 3b of the thin film reinforcing belt member 3 according to thepresent invention are embedded within the rigid resin reinforcing bodyhalves 2a and 2b is not limited to that shown in the embodimentsillustrated in FIGS. 1-9 where the respective outermost edge portions ofthe belt member 3 are terminated within the reinforcing body halves 2aand 2b, but the opposite side end portions 3a and 3b may be partlyprojected out of the reinforcing bodies 2a and 2b or alternatively maybe terminated just at the respective outer end surfaces of thereinforcing bodies 2a and 2b.

FIGS. 12 and 13 show an embodiment in which a corrugated pipe A having awavy pipe wall 1 is formed by using a laterally elongated belt body Bhaving a construction similar to that shown in FIG. 2.

The present invention is thus realized by setting the thickness andwidth of the belt body B and the thickness and the helical angle of thepipe wall 1 as desired, and hence the interval between the embeddedreinforcing bodies 2 can be set as desired by the setting of the shapeof the belt body B. Further, not only straight pipes as illustrated inthe embodiments shown in FIGS. 1-11, but also pipes in which the pipewall thereof is helically corrugated as shown in FIG. 13 can bemanufactured as desired. In addition, the helical corrugations can berealized not only in the form of regular arcuate corrugations, but alsoin the form of irregular arcuate, square, or triangular corrugations, orthe like.

FIGS. 14 and 15 show an embodiment in which it is possible to obtain apipe A arranged such that portions 1c project toward the inner surface11 of the pipe wall 1, as shown in FIG. 15, by using a belt body Bformed such that, as shown in FIG. 14, the length of each of the rigidresin reinforcing body halves 2a and 2b is made large in the verticaldirection between the bottom surface 111 and top surface 112 of the beltbody B which corresponds to the radial direction of the finished pipe A.Accordingly, the soft resin portion 1a of the belt body 3 has bulges 1cwhich project from the lower surface 111 of the belt body B at portionsthereof which are directly below the rigid resin reinforcing body halves2a and 2b. While the vertical or radial length of the reinforcing bodyhalves 2a and 2b is large in this embodiment, it is not always necessaryto make the vertical length large.

FIGS. 16 and 17 show another embodiment in which a belt body B isarranged such that, in addition to hard resin reinforcing body halves 2aand 2b formed at left and right ends of the belt body B, respectively,an additional hard synthetic resin reinforcing body 22 is embeddedintermediate of the left and right sides of the belt body B, and thethus arranged belt body B is used to form the pipe A in which the rigidsynthetic resin reinforcing bodies 2 and 22 are embedded in a pipe wall1 having roughly twice the pitch between adjacent joints, as shown inFIG. 17, than a pipe body in which the additional reinforcing body 22 isnot used. While in this embodiment the position of the additionalreinforcing body 22 is shown roughly midway between the reinforcing bodyhalves 2a and 2b, the position of the additional reinforcing body 22 maybe close to any one of the rigid resin reinforcing body halves 2a and2b.

In the same manner, a pipe having triple pitch reinforcing bodies alsocan be obtained by forming the rigid resin reinforcing bodies 22 at twopoints in the belt body B between the left and right reinforcing bodyhalves 2a and 2b.

In each of the embodiments described so far, for the sake ofconvenience, the shape of the outer end surface of each of the rigidresin reinforcing body halves 2a and 2b is illustrated to be linearlydivided by a bisector into two symmetrical left and right portions, butthe outer end surface of each of the rigid resin reinforcing body halves2a and 2b may be shaped so as to be reciprocally curved, or partlydepressed or projected, or otherwise uneven to increase the area ofabutment when the belt body 3 is wound and connected. Further, as shownin FIG. 18, it is possible to obtain a pipe arranged such that the leftand right reinforcing body halves 2a and 2b are made circular. Inaddition, adjacent right and left reinforcing body halves 2b and 2a aredisposed close to and in parallel with each other, and such that thepitch between adjacent ones of the reinforcing bodies 2 is twice that ofthe pitch that would otherwise exist, as shown by a dotted chain line inFIG. 18.

The typical embodiments according to the present invention have beendescribed above. However, the present invention is not limited to onlythe arrangement of those embodiments, as the invention and thoseembodiments can be suitably engaged and modified such that theconstituent features are still provided, the objects of the presentinvention are achieved, and the effects as described later are obtained.

As already is apparent from the above description of the presentinvention, in a conventional pressure-withstanding pipe, in spite of theprovision of the hard synthetic resin reinforcing bodies and the thinfilm reinforcing belt member in the pipe wall, the thickness of the pipewall at the portion in which the reinforcing body is embedded isunavoidably thicker than the rest of the pipe wall, as shown by the pipeillustrated in FIG. 19. This disadvantage can be eliminated by thepresent invention because the reinforcing belt member bridges andconnects the adjacent hard reinforcing bodies. The pressure-withstandingpipe according to the present invention is advantageous in that it ismade possible to manufacture a smooth pipe having a thin and uniformthickness and to reduce the amount of the materials used, and the weightof the entire pipe. In addition, as the reinforcing belt is firmly andsecurely held at its opposite side end portions by the hard reinforcingbodies, the reaction force of the pipe against any inner pressureexerted by a transported substance is extremely good over the entirecircumferential wall of the pipe. Particularly, the interval betweenadjacent reinforcing bodies can be kept at a predetermined value so asto prevent the pipe from being extended more than necessary orexcessively in a longitudinal direction. As a result, there is no riskthat the pipe wall will be made thin due to the extension action whichcould otherwise ultimately cause an exploding phenomenon. Moreover, dueto the hard reinforcing bodies, the resultant pipe has superior strengthagainst externally exerted pressure.

The method of manufacturing the pressure-withstanding pipe according tothe invention includes a step of extruding an extremely unique belt bodyfrom an extruding/molding machine. The unique belt body is arranged suchthat reinforcing body halves made of hard synthetic resin are embeddedin the belt body at the opposite side end portions of the belt body andalong the length of the belt body and the opposite side end portions ofthe reinforcing belt member are embedded in the reinforcing bodies so asto be held therebetween. The method also includes a further step ofhelically winding the extruded belt body while successively integrallyconnecting adjacent overlapping or abutting portions of the wound beltbody to thereby obtain the pipe. The invention thus has remarkableindustrial effects in that it is possible to easily obtainpressure-withstanding pipes which are extremely superior in structureand performance as described above, which can be manufactured easilythrough mass production, and which are low in cost.

What is claimed is:
 1. A method of manufacturing a pressure-withstandingpipe comprising the steps of:performing a single extrusion to produce apipe forming belt body from a first material, a second material harderthan said first material, and a belt-like third material, to obtain abelt body having at least first and second reinforcing members of saidsecond material embedded in said first material, with said belt-likethird material being embedded in said first material and secured to saidfirst and second reinforcing members so as to form a thin reinforcinglayer; and helically winding said belt body onto a pipe forming member,so that edges of said belt body are adjacent to one another.
 2. A methodof manufacturing a pressure-withstanding pipe according to claim 1,wherein said step of forming said pipe from said pipe forming belt bodycomprises the step of fusing said adjacent edges of said belt body toone another.
 3. A method of manufacturing a pressure-withstanding pipeaccording to claim 2, wherein said first and second reinforcing membershave a circular cross-section and are parallel to each other.
 4. Amethod of manufacturing a pressure-withstanding pipe according to claim2, wherein said steps of winding and fusing are performed immediatelyafter said step of extruding while said adjacent edges of said belt bodyare still substantially unhardened.
 5. A method of manufacturing apressure-withstanding pipe according to claim 2, wherein said firstmaterial is selected from the group consisting of a soft synthetic resinmaterial or a rubber material, and said second material is a syntheticresin material.
 6. A method of manufacturing a pressure-withstandingpipe according to claim 5, wherein said thin reinforcing layer issecured to said first and second reinforcing members by embedding firstand second opposite side end portions of said thin reinforcing layer insaid first and second reinforcing members, respectively.
 7. A method ofmanufacturing a pressure-withstanding pipe according to claim 6, whereinsaid pipe forming belt body has a first surface facing said pipe formingmember in said winding step, and said first and second reinforcingmembers are embedded in said belt body with at least said first surfaceof said belt body concealing said first and second reinforcing members.8. A method of manufacturing a pressure-withstanding pipe according toclaim 7, wherein said first and second reinforcing members are embeddedwithin said pipe forming belt body with said belt body substantiallycompletely concealing said first and second reinforcing members.
 9. Amethod of manufacturing a pressure-withstanding pipe according to claim7, wherein said adjacent edges of said belt body in said winding stepare either abutted or overlapped.
 10. A method of manufacturing apressure-withstanding pipe according to claim 7, wherein in said step ofextruding, said first and second reinforcing members are embedded closeto first and second edges of said belt body, respectively.
 11. A methodof manufacturing a pressure-withstanding pipe according to claim 10,wherein in said step of extruding said belt body, said first and secondreinforcing members are embedded with first and second areas thereof,respectively, exposed at said first and second sides of said belt body,respectively.
 12. A method of manufacturing a pressure-withstanding pipeaccording to claim 11, wherein said step of fusing comprises fusing saidfirst exposed area of said first reinforcing member with the secondexposed area of an adjacent second reinforcing member.
 13. A method ofmanufacturing a pressure-withstanding pipe according to claim 12,wherein said first and second exposed areas of said first and secondreinforcing members are substantially flat.
 14. A method ofmanufacturing a pressure-withstanding pipe according to claim 12,wherein said first and second exposed ares of said first and secondreinforcing members are non-planar and said first exposed area of saidfirst reinforcing member is shaped for receiving the exposed area ofsaid adjacent second reinforcing member.
 15. A method of manufacturing apressure-withstanding pipe according to claim 12, wherein said steps ofwinding and fusing further include:securing said first opposite side endportion of said thin reinforcing belt to said adjacent secondreinforcing member; and securing said second opposite side end portionof said thin reinforcing belt to an adjacent first reinforcing member,whereby said first and second opposite side end portions will be securedto two reinforcing members.
 16. A method of manufacturing apressure-withstanding pipe according to claim 12, wherein a distancebetween said first and second edges of said belt body is larger than athickness of said belt body.